Diffraction optics head up display

ABSTRACT

A head up display for combining a direct view as for example that of an aircraft pilot with superimposed light from another source by use of diffraction optics as a combining and collimating element. A specific implementation of an optical combining element and a secondary projector is also disclosed.

United States Patent 091 Antonson et al. 1 June 5, 1973 541 DIFFRACTIONOPTICS HEAD UP 3,499,703 3 1970 Bitetto ..350/l62 DISPLAY 3,446,9165/1969 Abel et al. ..356/25l I 1 mid Antonson, Vestal; John i'iiiifi35823 23322551... 1311;111:113:$12 262; gfigg gy fii g i h i z z3,522,980 8/l970 Lones ..350 172 9 Vestal, all of NY. FOREIGN PATENTS ORAPPLICATIONS [73] Assignee: General Electric Company, New 477,814 1/l938Great Britain ..l78/7.88

York, N .Y.

Primar ExaminerRonald L. Wibert 22 Pl d: 0 .14 1970 Y l 1 cc AssistantExaminer-Michael J. Tokar PP 97,891 Attarney-Francis K. Richwine, IrvingM. Freedman, Joseph B. Forman, Fran L. Neuhauser and Oscar B. 52 us. Cl.350/174, 350/35, 350/162 ZP Wadde" [51] Int. Cl. ..G02b 27/14 58 Fieldof Search ..350/125, 169, 174, ABSTRACT 162 ZP; 35/12 A head up displayfor combining a direct view as for 25; 343/6; 178/735 7'89; 356/251example that of an aircraft pilot with superimposed 353/12 '3 light fromanother source by use of diffraction optics as a combining andcollimating element. A specific [(56] References Cited implementation ofan optical combining element and a UNITED STATES PATENTS secondaryprojector is also disclosed. 3,633,988 [/1972 Farrar ..350/3.5 15Claims, 3 Drawing Figures PATENTEUJUH 5191s 3.737.212

INVENTORS ARVID L. ANTONSON, JOHN E. BIGELOW, CHARLES R. STEIN,

Xmas w. NHORN, a jam;

THEIR ATTORNEY.

BACKGROUND OF INVENTION 1. Field of Invention Sophistication in aircraftsystems has required development of improved means to provideinformation to pilots under conditions that do not distract the pilotfrom viewing visible air space and landscape. Such information is bestpresented and most easily assimilated as visual information within thenormal field of vision. The Heads-up-Display or HUD has as one solutionto this problem become a separate field of invention. One implementationof the HUD is by the positioning of a sheet of relatively transparentglass in the pilots normal field of view and at an angle so that lightprojected against a surface of the glass is reflected to the pilot. Theterm combining glass is derived from the fact of the combination ofplural optical images. The projected light can reproduce any of severalimages including for example instrumentation, symbology, viewaugmentation or view synthesization, generated by any of several meanssuch as light source or by raster scan or calligraphy in cathode raytubes. Among other uses HUD facilitates provision of an aiming point,sometimes in the form of an illuminated circular reticle, in armedmilitary aircraft.

2. Description of Prior Art Heads-up-Displays developed from flatreflective combining glasses to shaped combining glasses in combinationwith specialized projectors and the use of intermediate optical elementsto improve optical results by elimination of parallax and otherdeficiencies. Specific problems are recognized in the provision of anaiming device which must appear to the pilot to be at target range andmust be movable to permit incorporation of weapon adjustment for type ofweapon, gravity, and relative velocities of moving targets. Collimationof light to generate a virtual image at a distance has generally beenaccomplished by passing light through lenses prior to its reflectionfrom the combining glass. Accurate movement of an aiming point to definea proper line of sight has been approached in several ways includingmovable light sources, projection optics and specially shaped combiningglasses.

SUMMARY OF INVENTION The present invention in its generic formcontemplates the use of a diffracting optical element in a combiningglass to make use of diffraction phenomena to combine light with orwithout concurrent collimation. This also removes the necessity for andmakes optional certain additional optical elements often used as forexample collimation or other focusing of light transmitting an aimingpoint image prior to its reaching a combining glass. This invention,among other things, permits projection of the secondary image from therear of the combining element for better space utilization, permitssimpler designs and permits simultaneous transmission of both aimingpoint and view augmentation information. In addition to the broadconcept, the invention contemplates specific utilizations of curveddiffracting optical components containing systematically placeddeviations in optical properties, such as transparency, which deviationsmay be holographic recordings of either a point or an image incombination with a light source that may be a point or an illuminatedimage. A cathode'ray tube (CRT) may be used as a light source. Stillmore specifically the invention contemplates, for certain applications,utilization of a spherically curved diffracting optical component havingits convex surface placed toward the viewer and receiving projectedlight on its concave side from a CRT having a concave parabolic face.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graphic representation of theorganization of a heads up display in an aircraft cockpit and thecomponents of such display in a form representing the prior art.

FIG. 2 is a similar representation of a Heads-up- Display according toone embodiment of the present invention.

FIG. 3 is a graphic representation of the principles of diffraction andcollimation utilized in this invention.

DESCRIPTION OF PREFERRED EMBODIMENT FIG. 2 illustrates the applicationof this invention to a combining glass in an aircraft cockpit by use ofa diffracting optical component which for the purpose of explanationwill be referred to as a diffraction lens. The diffraction lens I asshown in vertical section is the curved implementation as indicated bythe visibility of the far edge 2 of the lens. The light providing theimage to be superimposed on the pilots field of vision through thewindshield 3 is provided by cathode ray tube 4. Normal straight aheadfield of vision of the pilot through the windshield is indicated bylines 5 and 6. The numeral 7 represents the instrument panel whichconstitutes one of the major obstructions in the placement of a HUDsystem and line 8 represents a clearance linefor pilot ejection, inwhich case of course canopy 9 would be removed. Although the inventionis illustrated in FIG. 2 in a highly developed specific embodimentwherein the diffraction lens" 1 is a convex spherical segment and theface 41 of the cooperating concept. This arrangement in which the lightproviding the image to be superimposed is projected onto the side of thelens remote from the pilot facilitates cockpit arrangement as easilycontrasted with the more conventional layout illustrated in FIG. 1. InFIG. 1 a conventional combining glass 11 is inserted at an angle to thepilots straight ahead" field of view as indicated by lines 51 and 61 andreceives light from a source as for example cathode ray tube 42 on thepilots side of the combining glass where it is projected by opticalelements represented by mirror 43 and lens 44. Some of the opticalelements in this case are necessitated for folding the projectionequipment into the space between instrument panel 7 and ejection line 8on one hand and the windshield 3. Comparison of FIGS. I and 2 providesan appreciation of one of the primary benefits of this invention whichis the assistance of cockpit layout. Less easily appreciated advantagesof the invention include the optical results and quality.

FIG. 3 is a graphic representation to facilitate explanation of theoptical properties incorporated into the diffraction lens 1 illustratedin FIG. 2. The projection lines radiating from a point source as from apoint on the face of the CRT are converted through action with the lensinto parallel lines indicating collimated light in the first orderdirection 15 as diffracted from the 0" order direction 14. These twophenomena are attributes of an optical element having systematicallyplaced deviations in optical properties such as opaque lines oralternating bands in the nature of a zone plate when those deviationsare selected to accomplish that result. The diffraction causes a bendingof the light to measurable angles from the original as indicated by raylines. In the instant application the first order (i.e. that closest tothe direct transmittal which is order) interference pattern is usedalthough any order other than 0 may be used and the optical qualities ofthe materials used selected to discourage higher orders or any undesiredorders of diffraction. The systematically placed deviations in opticalproperties in a transparent medium, which can be internal variations oftransparency, variations in optical thickness or be darkened orblackened lines applied to the exterior of the transparent material, ifin specialized curved form with dimensionally related distances betweendeviations can cause diffraction and can act as a lens to providecollimation or other focusing. (The term systematically placeddeviations in optical properties in a transparent medium and similardescriptive phrases or terms are used since there is no recognized namefor this class of optical elements producing usable diffraction patternswhich elements include of course special cases which are named such asdiffraction gratings, zone plates, etc.) The preferred deviation is ofthe pattern produced holographically by the projection of a point sourcebut a holographic projection of an image such as a reticle, althoughmore complicated, might be preferred for some applications. The best wayto make the kind of optical element desired for this use is byholography; specifically by holographic recording on photosensitivematerial of light projected from the selected point or image shapedsource. This has the side effect of compensating for dimensionalinaccuracies in curved plates such as the one used, which inaccuraciescould cause aberrations.

Utilization of adiffraction optics for this purpose is enhancedpractically as a result of the development of rare earth doped phosphorsfor cathode ray tubes. These materials permit high energies in narrowwavelength bands and therefore can be used to produce the intensemonochromatic light sources facilitating diffraction. Since one of theprimary objectives of this invention is to superimpose information ofthe nature of a reticle, circular or of other shape, or symbology in thenature of lines or figures representing attitude, altitude or otherflight parameters on a natural view, the monochromatic property of suchlight is also an aid to pilot recognition. Shaping of the diffractionlens 1 and of the face 41 of the CRT is appropriate to avoid parallaxthat could result from the somewhat different orientations and locationsof the source of the light as it is broadened or moved across the faceof the CRT. One specific solution to a specific application of theinvention derived from experimentation based on calculations resulted ina spherical diffraction lens and a concave paraboloidal CRT face whereinthe diffraction lens was of the relationship ofX Y 4 and the CRT facehad a curvature of Y 0.05485 X with the proper separation of the twoelements for cooperation. Although experimentation showed that thisproduced a useful accuracy and produced optical results on the order oftimes that of some other configurations used in experimentation, othergood implementations should be found,within these concepts.

This invention has peculiar applicability to aircraft weapons systemsand navigation or flight control aids in that an illuminated reticle orother visual aid projected as by a CRT can be moved about by means ofelectronic drives in the CRT to assume the proper position dependent onparameters of the weapons system or aircraft such as trajectories,range, velocities, attitude, altitude and relative movements of weaponand target so that the pilot may aim the weapon by flying the aircraftso as to maintain the reticle on the target or an auxiliary aiming pointor so that the pilot is assisted in other ways, e.g. to maintain adesired glide path on landing. In addition to these applications, theCRT projection onto the diffraction lens" without intervening opticsfacilitates the projection of view augmentation information, either realor scene generation, without the accuracy problems that could resultfrom optical elements which might be used to collimate light from areticle. With this system it is possible to add any of several differenttypes of view augmentation light including ordinary TV, narrow band TVsuch as IR, low light level TV or, with the necessary supportingelectronic equipment, radar sensed information or computed displays.

The foregoing description is based primarily on the use of substantiallymonochromatic light sources for reticles, symbology and even viewaugmentation. Use of monochromatic light simplifies implementation butis not a limitation on the system except for accuracy in the use ofcollimated reticles when allowing for some movement by the viewer.Information other than collimated, position significant, reticles can bedisplayed in multicolor form with, of course, each color having aslightly different angle of diffraction causing images to lie inslightly different planes.

It is also possible to add certain optical elements to correct forremaining optical aberrations including color aberrations withoutdetracting from the beneficial results of the invention. This latter,i.e. removal of color aberrations, would appear to make multicolorapplications of the invention possible with related colored images inaddition to the separately colored images.

We claim:

1. A combining glass for head up display equipment comprising an opticalelement having light diffracting properties in the form ofsystematically place deviations in optical properties which cause lightdiffraction for projecting the image of a separately presented object onone side of the glass at a position on the other side of the glass, saidcombining glass being substantially spherical in shape to correctoptical aberrations clue to difierent orientations and locations ofprojected light with spherical surface having curvature defined by X Y4.

2. ln head up display equipment having a first optical elementinterposed between a viewer and his real world view and a second opticalcomponent including means on one side of said first optical componentfor projecting light directly onto said first optical element wherebysaid light and said first optical element cooperate to create for theviewer a secondary image superimposed on said real world view, theimprovement comprising use of a-diffracting optical element as saidfirst optical element for projecting a secondary image on the other sideof said first optical element.

3. The combining glass of claim 1 wherein said element is also acollimator.

4. The improved heads up display equipment of claim 2 wherein saiddiffracting optical element used as said first optical element is adiffraction lens.

5. The combining glass of claim 1 wherein said ele' ment constitutes azone plate.

6. The combining glass of claim 1 wherein said systematically placeddeviations constitute a holographic recording of a light source and theprojection of light therethrough from a source on one side of said glasscollimates said light in the form of said source to focus the image ofsaid source at a near distance on the other side of said glass.

7. The improved equipment of claim 4 wherein said means for projectinglight includes means for emitting controlled frequency light of singleor multiple frequencies.

8. The improved equipment of claim 2 wherein said first optical elementis substantially transparent to the real world view but containssystematically placed deviations in optical properties so as to causediffraction phenomena in the light projected from said means forprojecting and to cause one order of diffraction of said light to createsaid secondary image in superimposition on said real world view.

9. The equipment of claim 8 wherein said deviations are in the form of aholographic recording of a light source.

10. The equipment of claim 8 wherein said first opti' cal element iscurved to correct optical aberrations due to different orientations andlocations of the said projected light and said second component includesa cathode ray tube having a curved face.

11. The equipment of claim 10 wherein the concave sides of saidcombining glass and said curved face are mutually facing.

12. The equipment of claim 11 wherein said combining glass issubstantially spherical and said face is substantially paraboloidal.

13. The equipment of claim 12 wherein said curvatures of said combiningglass and said face are related as approximately X Y 4 and Y= 0.05485 X14. The equipment of claim 9 wherein said light source, of which saiddeviations are a holographic recording, is a point source.

15. The equipment of claim 9 wherein said light source, of which saiddeviations are a holographic recording, is of the shape of an objectwhereby a'shaped secondary image may be created by projection of a pointsource by said means for projecting.

1. A combining glass for head up display equipment comprising an opticalelement having light diffracting properties in the form ofsystematically place deviations in optical properties which cause lightdiffraction for projecting the image of a separately presented object onone side of the glass at a position on the other side of the glass, saidcombining glass being substantially spherical in shape to correctoptical aberrations due to different orientations and locations ofprojected light with spherical surface having curvature defined by X2 +Y2
 4. 2. In head up display equipment having a first optical elementinterposed between a viewer and his real world view and a second opticalcomponent including means on one side of said first optical componentfor projecting light directly onto said first optical element wherebysaid light and said first optical element cooperate to create for theviewer a secondary image superimposed on said real world view, theimprovement comprising use of a diffracting optical element as saidfirst optical element for projecting a secondary image on the other sideof said first optical element.
 3. The combining glass of claim 1 whereinsaid element is also a collimator.
 4. The improved heads up displayequipment of claim 2 wherein said diffracting optical element used assaid first optical element is a diffraction lens.
 5. The combining glassof claim 1 wherein said element constitutes a zone plate.
 6. Thecombining glass of claim 1 wherein said systematically placed deviationsconstitute a holographic recording of a light source and the projectionof light therethrough from a source on one side of said glass collimatessaid light in the form of said source to focus the image of said sourceat a near distance on the other side of said glass.
 7. The improvedequipment of claim 4 wherein said means for projecting light includesmeans for emitting controlled frequency lighT of single or multiplefrequencies.
 8. The improved equipment of claim 2 wherein said firstoptical element is substantially transparent to the real world view butcontains systematically placed deviations in optical properties so as tocause diffraction phenomena in the light projected from said means forprojecting and to cause one order of diffraction of said light to createsaid secondary image in superimposition on said real world view.
 9. Theequipment of claim 8 wherein said deviations are in the form of aholographic recording of a light source.
 10. The equipment of claim 8wherein said first optical element is curved to correct opticalaberrations due to different orientations and locations of the saidprojected light and said second component includes a cathode ray tubehaving a curved face.
 11. The equipment of claim 10 wherein the concavesides of said combining glass and said curved face are mutually facing.12. The equipment of claim 11 wherein said combining glass issubstantially spherical and said face is substantially paraboloidal. 13.The equipment of claim 12 wherein said curvatures of said combiningglass and said face are related as approximately X2 + Y2 4 and Y 0.05485X2.
 14. The equipment of claim 9 wherein said light source, of whichsaid deviations are a holographic recording, is a point source.
 15. Theequipment of claim 9 wherein said light source, of which said deviationsare a holographic recording, is of the shape of an object whereby ashaped secondary image may be created by projection of a point source bysaid means for projecting.